1. Field of the Invention
The present invention relates to processes for treatment of waste sludges. More particularly, the present invention relates to processes that render biological waste sludges as pathogen-free, vector-free and sellable. Additionally, the present invention relates to waste treatment processes that utilize oxide-containing chemicals and pozzolanic materials for elevating the temperature of the mixed sludge and includes steps that pressurize the mixed sludge.
2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 37 CFR 1.98
In the past, various techniques have been developed for the purpose of sterilizing or decontaminating biological sludges and wastes. The most common process is the process of mixing lime with the sludge. The reaction of lime with the water in the sludge serves to elevate the temperature of the sludge for a maximum of 100° C.
U.S. Pat. Nos. 4,781,842 and 4,902,431, issued to Nicholson, teach a process to decontaminate wastewater sludge to a level that meets or exceeds U.S. EPA process standards. The process mixes sludge with an alkaline material sufficient to raise the pH of the end product to 12 or higher for at least one day. This process will raise the temperature to 50° C., but will not sterilize the sludge, nor does it eliminate the pathogenic microorganisms.
U.S. Pat. No. 4,306,978, issued to Wurtz, relates to a process of lime stabilization of wastewater treatment plant sludge. This patent discloses the dewatering of the sludge and intimately mixing calcium oxide to raise the temperature so as to produce a stabilized sludge particle.
None of these prior art inventions are capable of achieving temperatures, when mixed the sludge, of greater than 100° C. None of these prior art techniques allow for the shorter drying times as required by 40 C.F.R. Subchapter O, Part 503.32 a.311.A-D. The shorter drying times, as required by this Subchapter, are in accordance with the following formula:D=131,700,000/(1×10**0.14t)  (1)
where D=time in days
t=temperature in degrees Celsius
In the past, various patents have issued relating to process for treating a waste sludge of biological solids. The present inventor is an inventor of each of these prior process. For example, U.S. Pat. No. 5,635,069, issued on Jun. 3, 1997, describes a process for treating a waste sludge of biological solids that includes the steps of mixing the sludge with an oxide-containing chemical and sulfamic acid so as to elevate a temperature of the sludge, pressurizing the mixed sludge to a pressure of greater than 14.7 p.s.i.a. and discharging the pressurized mixed sludge. The oxide-containing chemical can be either calcium oxide, potassium oxide, or potassium hydroxide. The sludge has a water content of between 5 and 85 percent. The oxide-containing chemical and the acid are reacted with the sludge so as to elevate the temperature of the sludge to between 50° C. and 450° C. The pressurized mixed sludge is flashed across a restricting orifice or passed into a chamber having a lower pressure.
U.S. Pat. No. 5,868,942, issued on Feb. 9, 1999, teaches a process for treating a pathogen-containing sludge of biological solids which includes the steps of mixing the sludge with calcium oxide, ammonia and carbon dioxide so as to elevate a temperature of the mixed sludge to between 50° C. and 140° C. and which elevates a pH of the mixed sludge to greater than 9.8. The process also includes the steps of pressurizing the mixed sludge to a pressure of greater than 14.7 p.s.i.a. and discharging the pressurized mixed sludge. Ammonia is added to the sludge in the form of either ammonia gas, ammonium hydroxide, ammonium bicarbonate or as a byproduct of the reaction of the calcium oxide with the water in the sludge. Carbon dioxide is added to the sludge in the form of carbon dioxide gas or a reactant of ammonium bicarbonate. The pressurized mixed sludge is discharged by flashing the sludge across a restricting orifice and by evaporating a liquid component of the flashed sludge.
U.S. Pat. No. 6,056,880, issued on May 2, 2000, describes another process for treating a waste sludge of biological solids. This process includes the steps of blending the sludge with an acid, mixing an oxide-chemical with the blended sludge so as to cause a reaction which elevates a temperature of the sludge, pressurizing the mixed sludge to a pressure of greater than 14.7 p.s.i.a. and retaining the mixed sludge at such pressure for a period of time of no less than 15 seconds. The pressurized mixed sludge is then discharged. The step of pressurizing is accomplished by passing the mixed sludge as a flow into the pipe. The pipe has a length and diameter such that the flow of the mixed sludge takes longer than 15 seconds to pass through the pipe. The mixed sludge is heated as the flow passes through the pipe. An immersion heater or a magnetic field is installed so as to apply heat directly to the mixed sludge as the mixed sludge passes through the pipe.
U.S. Pat. No. 6,214,064, issued on Apr. 10, 2001, describes a process for making a fuel product by blending a sewage sludge with an acid, mixing an oxide-containing chemical with the blended sludge so as to cause a reaction which elevates a temperature of the sludge, pressurizing the mixed sludge to a pressure of greater than 14.7 p.s.i.a. for a period of time of no less than 15 seconds, mixing the pressurized mixed sludge with coal fines, and solidifying the mixture of pressurized mixed sludge and coal fines. The oxide-containing chemical is either calcium oxide or calcium hydroxide. The acid is sulfamic acid.
It is an object of the present invention to provide a process for rendering a biological waste sludge pathogen-free and vector-free.
It is another object of the present invention to provide a process that converts the biological waste sludge into a sellable end product.
It is still a further object of the present invention to provide a process that eliminates or reduces waste incineration and landfilling of waste sludges.
It is another object of the present invention to provide a process that eliminates the odors resulting from lime stabilization.
It is still a further object of the present invention to provide a process that facilitates the dewatering of the biological sludge.
It is still another object of the present invention to provide a process that recycles waste heat.
It is still a further object of the present invention to provide a process for treating waste sludges that is cost effective, easy to use, and easy to install.
These and other objects and advantages of the present invention will become apparent from a reading of the attached specification and appended claims.